Our overall objective is to understand the physiological interactions between the circadian and reproductive systems of mammals. Using the golden hamster as our primary model, we plan three distinct approaches that will, when brought together, yield a coherent picture of important aspects of these interactions. In the first, we will investigate the role of the suprchiasmatic nucleus (SCN) by directly measuring its circadian rhythm of 2-deoxy-D-glucose uptake under various lighting conditions that have known effects on the reproductive system. We will assess the effect of pinealectomy and exogenous melatonin on SCN rhythmicity as well as the effects of steroid hormones known to affect circadian locomotor rhythmicity. In other experiments we will test the hypothesis that the SCN is a driving oscillator in the circadian system by measuring the wave form of its metabolic response to light and temperature pulses. We will also investigate the role of the SCN in the generation of ultradian rhythms. The second approach involves extension and refinement of present knowledge of the effects steroid on locomotor rhythmicity. Does estradiol, which is known to have effects when administered chronically via silastic capsules, exert differential effects when administered by injection at different circadia times? Doos progesterone have an effect on the response to estradiol? To what extent do the circadian differences between males and females that we have recently discovered, depend on differences in titers of circulating hormones? To what extent are they produced during development? Our third approach is a set of experiments designed to provide basic information about the development of circadian rhythmicity. We will investigate the role of the mother in several ways including artificial rearing as well as the effects of rearing on light cycles with periods different from 24. We will test the effects of neonatal castration and androgen treatment on the subsequent rhythmicity of the adults. Finally, we will study the time course of the appearance of SCN rhythmiity and of its light and hormone sensitivities.